Aluminum is one of the most widely distributed elements in the earth's crust and is a philophilic, philic, and oxygen-friendly element. Aluminium is found in nature as oxides, hydroxides, and oxygen-containing aluminosilicates, and aluminum is rarely found in natural metals.
There are 258 kinds of aluminum-containing minerals known in nature, of which about 43 are common minerals. In fact, there is no aluminum deposit consisting of pure minerals, which are generally symbiotic and mixed with impurities. From an economic and technical point of view, not all aluminum-containing minerals can be used as industrial raw materials. The metal used to extract the aluminum is mainly bauxite consisting of diaspore, boehmite or gibbsite. Due to the lack of bauxite resources, the former Soviet Union used nepheline and alum to refine alumina. China's sulphoaluminium antimony ore can comprehensively recover alumina.
The diaspore is also known as diaspore. Its structural formula and molecular formula are AlO(OH) and Al2O3·H2O, respectively. Orthorhombic system, crystallized well was columnar, plate-like, scaly, acicular, prismatic and so on. The diaspores in the ore generally contain different amounts of isomorphous contaminants such as TiO2, SiO2, Fe2O3, Ga2O3, Nb2O5, Ta2O5, and TR2O3. Diaspore is soluble in acid and alkali, but it dissolves very weakly under normal temperature and pressure. It needs to be completely decomposed under high temperature and high pressure and strong acid or strong alkali concentration. Diaspore is formed in an acidic medium and is symbiotic with boehmite, hematite, goethite, kaolinite, chlorite, and pyrite. Its hydration can become gibbsite, dehydration can become α corundum, can be kaolinite, pyrite, siderite, chlorite, etc.
The boehmite monohydrate is also known as boehmite and boehmite. Its structural formula is AlO(OH) and its molecular formula is Al2O3·H2O. Orthorhombic system, crystallized well was diamond, prismatic, prismatic, acicular, fibrous and hexagonal plate. The ore boehmite in the ore often contains Fe2O3, TiO2, Cr2O, Ga2O3, and the like. The boehmite is soluble in acid and alkali. The mineral is formed in an acidic medium and is mainly produced in the sediment of bauxite, which is characterized by the symbiosis with siderite. It can be represented by diaspore, gibbsite, kaolinite, etc. Dehydration can be converted into diaspore and alpha corundum, and hydration can become gibbsite.
The gibbsite is also known as hydrated bauxite, borosilicate, structural formula Al(OH), molecular formula is Al2O3·3H2O. Monoclinic crystals, crystallized in perfect hexagonal plate, prismatic, often fine crystal aggregates or twins, ore silicates are mostly irregular aggregates, all contain different amounts of TiO2, SiO2 , Fe2O3, Nb2O5, Ta2O5, Ga2O3 and other isomorphous or mechanical inclusions. The gibbsite is soluble in acid and alkali, and its powder is heated to 100° C. and completely dissolved in 2 hours. The mineral is formed in an acidic medium, and gibbsite is a primary mineral in the weathering crust deposit, and is also a main ore mineral, which is symbiotic with kaolinite, goethite, hematite, and illite. The dehydration of gibbsite can be converted into boehmite, diaspore and α-corundum, which can be accounted for by kaolinite, halloysite, and the like.
The chemical composition of bauxite is mainly Al2O3, SiO2, Fe2O3, TiO2, and H2O+. The total of these five components accounts for more than 95% of the components, and is generally >98%. The minor components are S, CaO, MgO, K2O, Na2O, CO2, MnO2, organic matter, carbonaceous, etc., trace components include Ga, Ge, Nb, Ta, TR, Co, Zr, V, P, Cr, Ni, and the like. Al2O3 mainly occurs in aluminum minerals - diaspore, boehmite, and gibbsite, and secondly in silicon minerals (mainly kaolinite minerals).
Under endogenous conditions, due to the widespread presence of silica, Al2O3 and SiO2 are often tightly combined into various types of aluminosilicate minerals. These minerals generally have a ratio of aluminum to silicon of less than one, and industrial requirements for aluminum ore generally require Al2O3 ≥ 40%. Since Al/Si is from 1.8 to 2.6, industrial aluminum deposits are rarely formed under endogenous conditions.
At present, the known industrial bauxite mines at home and abroad are mostly formed under superficial conditions. There are two main forms of bauxite production under supergene conditions: weathering-residual (yu) mineralization (red earth mineralization) and weathering-handling-sedimentary mineralization or weathering-reformation-redeposition mineralization (sedimentation mine). Weathering-residual (remnant) mineralization is a favorable terrain (such as residual mounds, low mountains, and mesa) where aluminum-containing parent rocks excrete under hot and humid climate conditions. Due to the weathering decomposition of water, CO2, and living organisms, the parent rock The easily soluble materials K, Na, Ca, Mg, and SiO2 were lost and discharged, and the less active substances Al, Fe, and Ti remained in situ to form lateritic bauxite. Weathering-handling-sedimentary ore deposits are aluminum-bearing rocks, lateritic weathered crusts or formed laterite deposits, which are mechanically or chemically weathered and denuded by gravity, water and natural acids (sulfuric acid, carbonic acid, organic acids). Physical and chemical transformations such as transportation and transportation are used to form bauxite deposits in hilly depressions, valleys, offshore lake basins, or coastal lakes and confined basins, and to form sedimentary bauxite deposits in an aqueous environment.
Bauxite ore contains useful components such as yttrium, vanadium, niobium, tantalum, titanium, niobium, and radioactive elements, and these valuable accompanying components can be comprehensively recovered. The sulfur, CO2, MgO, and P2O5 in the ore are harmful components that are not conducive to the smelting and recovery of aluminum.
Bauxite ore is classified according to the main aluminous minerals it contains: gibbsite type, boehmite type, and dicalouscite type. The foreign bauxite ore is mainly sesquisite type, followed by boehmite type, and there is very little diaspore type bauxite. However, our country is mainly a diaspore type bauxite, and there are very few gibbsite type bauxite mines.
The foreign gibbsite type bauxite ores are characterized by high aluminum, low silicon, and high iron. The quality of ore is good, and it is suitable for Bayer process with low energy consumption. China's diaspore-type bauxite is generally characterized by high aluminum, high silicon, low-sulfur and low-iron, and low-to-low aluminum-silicon-silicon ratio. The quality of ore is poor, and it is difficult to process. The aluminum oxide production uses multiple methods with high energy consumption. .
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